Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.73   13.431%   $96.1101   $96.11   $96.10   $96.10  
  Purchase #2 $98.37   10.221%   $108.4244   $108.42   $108.40   $108.40  
  Purchase #3 $74.41   4.340%   $77.6394   $77.64   $77.65   $77.60  
  Purchase #4 $42.91   10.270%   $47.3169   $47.32   $47.30   $47.30  
  Purchase #5 $66.87   10.106%   $73.6279   $73.63   $73.65   $73.60  
  Purchase #6 $151.71   10.426%   $167.5273   $167.53   $167.55   $167.50  
  Purchase #7 $78.31   10.203%   $86.3   $86.30   $86.30   $86.30  
  7 purchase totals = $597.31       $656.9460   $656.95   $656.95   $656.80